1. Field of the Invention
This invention relates to the used of a copper-base alloy containing 4 to 6% nickel, 4 to 6% aluminum balance copper and inevitable impurities due to the manufacture, as a material for use in the making of coins or the like which are required to have a golden color and a high resistance to tarnishing.
2. Discussion of Prior Art
The inflationary tendencies which have prevailed throughout the world for years and differ in strength in various countries, and the considerable increase of transactions effected with the aid of machines for vending merchandize and services, have resulted in a need for coins having a high value. For instance, the introduction of a 10-mark coin has been considered in Germany for some time. In most of the existing systems of coins, it would not be practicable to provide larger coins for a distinction from the most valuable existing coins because the heavier weight and the larger volume would render the handling more difficult. Additionally, the larger coins would require a considerable quantity of metal. Moreover, rising prices of the metals which can be used in coins will have the result to decrease the difference between the metal value and the face value of the coins. For this reason the public authorities who are responsible for the coinage consider the issuing of new coins which have higher values and are smaller and differ in color from the most valuable existing coins. Gold colors are particularly desirable for such purpose because they are associated with a high value and most coins in circulation, at least those having high values, are silver-colored.
Coin materials having a goldlike color are known and some of them have already been used. They consist almost without exception of copper-base alloys, which contain, e.g., 25% zinc, or 20% zinc and 1% nickel, or 5 to 6% aluminum and 2% nickel, or 2% aluminum and 6% nickel. These materials have the disadvantage that they lose their original bright appearance rather quickly in use and assume a dull color having a brownish tinge. Whereas this disadvantage is tolerated with coins having low values, a rapid discoloration of highly valuable coins in use is not acceptable. For this reason, silver-colored materials, particularly nickel alloys, have previously been used for coins of high values.
It is desired to provide a gold-colored material which can be used to make coins or the like and call well be processed to make coins by casting, rolling and stamping and has a high resistance to tarnishing so that it retains as long as possible the original golden color.